Crystalline Solids

INTRODUCTION
There are two types of solids depending on type of arrangement of atoms in crystal lattice – crystalline and amorphous. Crystalline solids have definite geometric forms because of the orderly arrangement of the atoms whereas amorphous solids have their atoms arranged randomly throughout the solid. Glass is an amorphous solid material. It is composed of several inorganic materials present in varying proportion. Some are added intentionally whereas others are present un-intentionally as contaminant (which often aids an analyst in establishing origin of glass fragment). It is a hard and brittle substance made of sand i.e. silicon oxides mixed with various metal oxides. When sand mixed with metal oxides is melted at high temperature

If these physical properties match then the examination is carried on otherwise it is stopped over here and it is evident that both glass fragments do not match and are from different origin.
• After the physical properties are matched, optical properties like refractive index and density of both glass fragments are measured and compared. If these properties do not match the examination is terminated here itself and report is submitted that both fragments are from different origin whereas if these properties do match then the next step is followed.
• The next step in glass fragments examination is elemental analysis of both the fragments using various techniques like SEM, XRF, and ICP. This is the final step in glass fragments examination and if the elemental analysis results of both fragments match then it is proved that both the glass fragments are from same origin.
GLASS FRACTURES
Glass bends in response to any force that is exerted on its sur¬faces; when the limit of its elasticity is reached, the glass fractures. There are two types of glass

Determination of direction of force It is done by determining radial fractures lying within the first concentric fracture firstly. If the edges of concentric and radial fractures are observed properly then some cracks called stress marking are observed. Stress marks are arch shaped and are perpendicular to one surface and parallel to the other. Examination of stress marks is important due to the fact that their perpendicular edge always faces the surface from which the respective crack had originated. Thus the perpendicular end of stress marks which are present on the edge of radial cracks is always opposite to the side from which force was applied whereas in case of concentric fractures the perpendicular end faces the surface from which the crack